If, in a triangle, angles α, β, γ lie opposite the sides of length a, b, c, then (EWD) sign(α β - γ) = sign(a² b² - c²), where sign(t) is the The most famous of right-angled triangles, the one with dimensions 3:4:5, has been sighted in Gothic Art and can be obtained by paper folding.

Rather inadvertently, it pops up in several Sangaku problems. The proof has been illustrated by an award winning Java applet written by Jim Morey.

Finally, the two rectangles AELM and BMLD make up the square on the hypotenuse AB. At this point we therefore have two triangles and a strange looking shape.

Besides the statement of the Pythagorean theorem, Bride's chair has many interesting properties, many quite elementary. Dijkstra found an absolutely stunning generalization of the Pythagorean theorem.Below is a collection of 118 approaches to proving the theorem.Many of the proofs are accompanied by interactive Java illustrations. C.) or someone else from his School was the first to discover its proof can't be claimed with any degree of credibility. C.) by an early 20th century professor Elisha Scott Loomis.The right one is rotated clockwise whereas the left triangle is rotated counterclockwise. ibn Qurra's diagram is similar to that in proof #27.Obviously the resulting shape is a square with the side c and area c². (A variant of this proof is found in an extant manuscript by Thâbit ibn Qurra located in the library of Aya Sofya Musium in Turkey, registered under the number 4832. The proof itself starts with noting the presence of four equal right triangles surrounding a strangely looking shape as in the current proof #2.Three of these have been rotated 90°, 180°, and 270°, respectively. Let's put them together without additional rotations so that they form a square with side c.The square has a square hole with the side and a hole with the side c.The theorem is of fundamental importance in Euclidean Geometry where it serves as a basis for the definition of distance between two points.It's so basic and well known that, I believe, anyone who took geometry classes in high school couldn't fail to remember it long after other math notions got thoroughly forgotten.On the other hand, ΔAEC has AE and the altitude from C equal to AM, where M is the point of intersection of AB with the line CL parallel to AE.Thus the area of ΔAEC equals half that of the rectangle AELM.We can compute the area of the big square in two ways.Thus (a b)² = 4·ab/2 c² simplifying which we get the needed identity.ΔABF has base AF and the altitude from B equal to AC.